The present invention generally relates to the assessment or quantitative evaluation of the amount of radiation delivered to an object undergoing sterilization in situ.
Providing a food supply that is safe for consumption can be problematic, particularly because suitable control measures can be hard to enforce as the producers, distribution chains, and markets become more global. In addition, visual inspections are not always reliable as a means of detecting harmful contaminants. Further, cross contamination of foods can occur during handling (including during harvesting, shipping, and packaging), that can infect food typically believed to be relatively safe from pathogens. For example, E. coli bacteria, which is typically found in certain meats, can also be found in xe2x80x9cfreshxe2x80x9d vegetables and fruits. The presence of atypical bacteria in foods can be attributed to the use of particular types of fertilizers or to processing conditions. Certain processing conditions may allow direct contact of various food items with contaminated products, while others may allow for indirect contamination such as via contact with contaminated containers or work surfaces, each of which can allow the undesirable spreading of contaminants.
Certain safety precautions can be taken to reduce the risk of illness associated with the consumption of foods which may carry pathogens, such as washing the fruit and vegetables before consumption and/or cooking meat or other food items to or above a certain temperature. While washing vegetables and fruits can dilute or remove the contaminant(s) from the food, and cooking the food to a temperature sufficient to kill the bacteria may reduce the exposure risk, not all foodstuffs are washed or properly cooked before they are eaten. Further, children can be especially vulnerable to harmful exposures, as many do not reliably pursue these safety measures and exposure to relatively small amounts of harmful contaminants can be more profound relative to healthy adults. A consumer has little control over what safety steps (i.e., washing and/or cooking food properly), are followed by personnel at a food service outlet.
Processing foods to reduce or even eliminate unwanted microorganisms can be an important step forward in the reduction and elimination of the risk of illness due to exposures to contaminated foods. One economic and effective way to rid food of contaminating microorganisms is to irradiate food with ionizing radiation to effectively xe2x80x9csterilizexe2x80x9d the food to destroy the harmful microorganisms therein (irradiation can be used to sterilize other objects such as medical devices). This can be an effective and economic tool in improving the safety of the food supply to thereby provide safe, sterilized food items which have reduced (and potentially even undetectable) levels of harmful microorganisms.
Generally stated, there are two primary modalities used to irradiate food and other items to achieve sterilization. One modality includes the use of a radioactive element such as Cobalt-60, and the other employs electron beams produced by a linear accelerator. The radiation dose should be monitored to ensue that pathogens are destroyed effectively. For food or edible items, radiation doses in the 0.15 kGy to 10 kGy range are typically used, while for devices and objects, radiation doses are higher, typically up to 20 kGy or more.
Conventionally, in order to monitor the radiation doses provided by the irradiation process, either TLD""s (thermoluminescent devices) or chromatic tags are used. TLD""s can be generally described as crystals, e.g., lithium fluoride, the structure of which is changed (damaged) during exposure to radiation. More particularly, during irradiation, electrons travel to and are trapped in the crystal after being ejected by the high-energy (ionizing) photons used for sterilization. Upon exposure to heat, the electrons in the crystal fall back to their ground states and emit light as result of the change. A spectrophotometer is used to measure this light and provide a quantitative assessment of the amount of radiation to which the device was exposed. A technician typically recovers the TLD from an irradiated package and then analyzes/measures the emitted light on the spectrophotometer. Unfortunately, this process can be relatively labor-intensive and can be undesirable for use in a mass production environment.
Chromatic tags can be described as plastic tags (formed of materials such as PMMA) which undergo a color change upon exposure to radiation at some level. However, generally stated, the color change is often a subjective evaluation when done visually by an inspector. To receive a more reliable assessment, colormetric readers are used to quantify the color change to a more exact level. This can be compared to the use of radiographic film wherein the level of exposure on the film corresponds to the intensity of the dose received. Unfortunately, again, the determination of the dose measured in this manner can also be labor intensive and/or unsuitable for a mass-production environment.
It is therefore an object of the present invention to provide a cost-effective dosimeter, which can be used to evaluate the radiation dose delivered to an item undergoing sterilization.
It is yet another object of the present invention to provide improved methods to evaluate a radiation dose(s) delivered to a plurality of sterilized packaged food items without requiring direct human intervention.
It is a further object of the present invention to provide economic methods and devices which are suitable for mass-production environments and which can automatically relay and/or correlate production and/or process information to an irradiation dose.
It is an additional object of the present invention to provide an economic automated method of determining the amount of radiation delivered to an item in situ.
It is another object of the present invention to provide an economic dosimeter configuration, the sensing element of which can be embedded in a packaged and/or sealed food or medical item.
These and other objects can be satisfied by the present invention by a radiation dosimeter which is adapted to change the value of an associated electronic parameter in a detectable manner dependent upon the amount of radiation it is exposed to. The value of the electronic parameter can be relayed automatically (or semi-automatically) and used to determine and provide the radiation dose for a sterilized item, preferably a food or edible item, without requiring human intervention. The sensor can be configured as a single use, disposable, passively operated wireless or telemetrically operated sensor.
More particularly, a first aspect of the invention is a method for determining the irradiation dose delivered to an object. The method includes the steps of (a) irradiating at least one object with a radiation dose which is sufficient to sterilize the object; (b) positioning a sensor on the object such that it is held proximate the object during the irradiating step, the sensor has associated operational parameters, and one or more of the operational parameters is configured to change responsive to the irradiating step; (c) transmitting data associated with the operational change in the parameter of the sensor; and (d) determining the radiation exposure dose based on the data provided by the transmitting step. In certain embodiments, the transmitting step can be performed such that is carried out by a wireless or telemetric transmission.
A second aspect of the present invention is a radiation dose evaluation system. The system includes a radiation source and at least one dosimeter sensor adapted to be positioned on an object undergoing irradiation treatment such that the sensor is exposed to an amount of radiation representative of the amount of radiation exposure introduced to the object. The system also includes a wireless or telemetric reader operably associated with the sensor such that it receives data associated with the sensor and a controller operably associated with the reader. The system also includes a computer program operably associated with the controller. The computer program can be configured to analyze data transmitted from the sensor to the reader or receiver to determine a radiation dose associated therewith.
In certain embodiments, the system is configured to evaluate radiation levels above about 0.1 kGy, and typically for food or edible items, in a range of from about 0.15-10 kGy (with pet and animal foods, spices, melon, herbs and seasonings approved up to about 30 kGy), but more typically about 1-7 kGy, and for other sterilized items such as medical implements and devices in a range of from about 10-50 kGy.
Another aspect of the present invention is a passively operated (it does not require a power source such as its own battery) radiation dose sensor. The sensor includes a xe2x80x9ctankxe2x80x9d circuit which, in operation, is configured to provide an electrical output that changes in a predictable (dose-correlated) manner when exposed to radiation in the desired irradiation dose range (for many food items above about 0.1 kGy, and more preferably in the 0.1-10 kGy range). The sensor tank circuit includes a capacitor and an inductor operably associated with the capacitor. In operation, the sensor is passively configured to be inductively powered by a remote reader/receiver (without requiring a battery or voltage regular or discrete power source on the sensor itself). Thus, the sensor is configured such that it alters at least one electrical property responsive to the amount of exposure to radiation which is then used to determine the amount of radiation the sensor receives (and/or is exposed to).
In certain embodiments, the sensor is passively configured to provide a reflected signal output and has an electronic circuit comprising a MOS device such as a MOS capacitor or FET structure semiconductor device configured to withstand and provide a wireless or telemetrically detectable radiation sensitive output responsive to particular levels of irradiation exposure (for most food items, the operational range is in about the 0.1-10 kGy range, see FIG. 1B). In other embodiments, the electronic circuit comprises other components and parameters to evaluate radiation dose, such as the Hfe or xcex2 of a bipolar transistor or the leakage current of a diode or the coupling factor (K) between primary and secondary circuits.
In certain embodiments, the sensor circuit semiconductor or MOS device is a RADFET which is sensitive in the irradiation dose range being monitored (i.e., it has a suitable rad-hardness corresponding to the food item undergoing electronic sterilization). The RADFET is operably associated with a flat form coil (typically secured or bonded to a copper or foil or mylar coil). The sensor circuit has a pre-irradiation exposure threshold voltage value and a threshold voltage which varies corresponding to the irradiation level to which it is exposed. The threshold voltage can be used to determine the radiation dose delivered to the sensor (and with the sensor on or in proximity to the product, to the product itself).
The detection system can be configured to detect other electronic outputs or parameters. For example, the sensor tank circuit can have a detectable first resonant frequency prior to exposure to radiation above a threshold level, and a plurality of altered or changed resonant frequencies different from the first resonant frequency corresponding to the amount of radiation exposure it experiences above the threshold level. Alternatively, or in addition to, the sensor electronic circuit can be configured such that it alters its Q factor based on exposure to radiation and, as such, the Q factor values can then correlated to the radiation exposure level to determine the associated radiation dose.
In an alternative embodiment, the sensor tank circuit can be configured with a capacitor having a central dielectric formed of a material which changes one or more of its conductivity, capacitance value, or dielectric constant responsive to radiation exposure level.
As noted above, for edible items, the sensor is preferably configured to detect radiation doses in the range of from about 0.1-10 kGy, and more preferably about 0.5-10 kGy and for other items such as medical devices, the sensor is preferably configured to detect radiation doses in the range of from about 10-50 kGy. Of course, application specific sensors or sensors which operate in more narrow ranges within the overall range of interest (suitable for more than one product type) can also be provided to allow for a more narrow radiation sensitive sensor (i.e., one for beef and/or poultry, one for pet food, one for fruit, one for grains, etc., or a 0.1-0.5 kGy, a 0.5-2 kGy, a 2-4 kGy, a 1-4 kGy, a 2-5 kGy, and the like).
The sensor may also be configured with a low profile when viewed from the side to allow for easier processing and a reduced likelihood of handling damage which may occur in a mass production environment. Indeed, the sensor may be integrated into a package configured to hold the object undergoing irradiation. The package may be sealed with the sensor thereon or therein prior to irradiation.
Another aspect of the invention is a method for determining the radiation dose of a product. The method includes the steps of (a) positioning a sensor with a tank circuit on an object; and (b) irradiating the object and the sensor to a level which is sufficient to sterilize the object and to induce alteration in a predetermined operational parameter of the sensor, the degree of alteration representative of the amount of irradiation received by the sensor. The data may be wirelessly transmitted from the sensor to a receiver.
In certain embodiments, the object is sealed within a container prior to irradiation so as to reduce the likelihood of exposure to airborne or other contaminants after the sterilization process.
The present invention provides cost-effective irradiation dosimeter systems and dosimeter sensors that can be employed in a mass production environment. The systems and sensors can be used to quantify or evaluate radiation exposure or doses for items which have been electronically pasteurized to prepare and process uncooked and frozen commercial sized and/or bulk food items for safer consumption. The system can also be used to monitor irradiation delivered to inhibit the decay of food items conventionally introduced by microorganisms living therein, thereby reducing the amount of food which conventionally has been unable to be sold due to undesirable decay and/or spoilage. The system reduces inspection labor requirements (eliminating the requirement of visual inspection or physical intervention to determine the dose) and can improve the reliability of the production process itself by providing radiation dose information on a substantially real-time basis to allow faster adjustment of process parameters. The system can be used in cold environments (where food is refrigerated or frozen), ambient, and hot (where food is cooked) environments.
The foregoing and other objects and aspects of the present invention are explained in detail in the specification set forth below.